Various types have been hitherto proposed as the pipe connecting member for burying a coil heated by energization in a joint main body.
For example, as known in the pipe connecting member disclosed in the Japanese Patent Publication No. 4429/1958, coils are buried in the end portions of a branch pipe formed in a T-shape or pipe bodies in various shapes, and by energizing the individual coils with the end portion of resin pipe inserted in each end portion of the pipe body, the end portions of the resin pipes are connected.
In the case of this pipe connecting member, however, since the coils are directly buried in the end portions of the pipe body formed by injection molding or the like to form in one body, every time the diameter of the resin pipe to be connected is changed, the pipe connecting member suited to the diameter is required. That is, these pipe connecting members must be manufactured all in different molds in order to prepare multiple pipe connecting members suited to a variety of resin pipes, and hence the productivity is poor and it is not rational.
Accordingly, for example as shown in the Japanese Patent Publication No. 40743/1989, other pipe connecting member is proposed, in which the coil is buried in the entire inner circumference of the joint main body, and by energizing the coil with the end portions of the resin pipes inserted from both side of the joint main body, the resin pipes are connected freely.
In this case, although the resin pipes of various diameters may be directly connected, the resin pipes connected in the joint main body must be held and fused at once, and the installation work is complicated and the installation time is long. Besides, since the resin pipes inserted from both ends of the joint main body are fused at once, a large electric power is required in the case of resin pipe of a large diameter. If a large electric power is not available, at a lower electric power, the energization time must be extended to fuse.
It is therefore attempted, as disclosed in the Japanese Patent Provisional Publication No. 500452/1989, to use a resin pipe preliminarily having an electro-fusion function at one end. That is, in this resin pipe, one end is dilated, and a coil heated by energization is inserted in the dilated part, and the end portion of each pipe body is inserted into the dilated part to fuse.
In the case of this resin pipe, however, since one end is dilated, the wall thickness decreases in the dilated part, and a sufficient strength is not obtained. Besides, the residual stress at the time of dilating is large, and shrinkage may take place in the course of time after dilating, and a sufficient dimensional precision may not be obtained. Yet, although the coil is disposed in the dilated part by inserting the coil at the time of dilating and then cooling, it is not formed sufficiently in one body substantially, and enough fusion is not attained when fusing.
When connecting the resin pipe forming a joint part in various shapes such as flange surface to the pipe connecting members described above, it is necessary to connect an intermediate member to the pipe connecting member after interposing the intermediate member possessing a flange surface that can be connected with the flange surface, which results in a spliced piping. As a result, the cost for connection and installation expense are increased. Similarly, when one resin pipe is made of polyethylene and the other resin pipe is made of vinyl chloride, they cannot be directly fused, and a spliced piping is inevitable.
Furthermore, when connecting the resin pipes by using such pipe connecting members, marking job is required before fusing, which is also annoying. Besides, the marking job serves only for discovering deviation in resin pipes, and will not prevent deviation. In the fusion work, therefore, the resin pipes must be fixed with jigs to prevent from slipping out of the pipe connecting member, and it is always required to carry jigs.
The invention is devised in the light of such background, and is hence intended to present a pipe connecting member excellent in productivity and installation efficiency in various pipes, and capable of performing fusion job easily and simply.